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Re: How to send a onetime scheduled task to executorService that has a repeptitive task ongoing

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Thu, 10 Mar 2022 04:32:40 -0800 (PST), /mike/:

> This service will send a message every 10 seconds to a server and if we get a response then we are ok and connection is considered ok.
> 
>              future = scheduledTaskExecutor.newScheduledTask(keepAlive, 0, properties.getKeepAliveTime(),
>                      TimeUnit.SECONDS);
> 
> Note: newScheduledTask() calls ScheduledFuture<?> future = executorService.scheduleAtFixedRate(runnable, delay, period, timeUnit);
> 
> However we also have a method where we "instantly" want to find out if we are connected to the server.
> 
>              ScheduledFuture<?> scheduledTaskOnce = scheduledTaskExecutor.newScheduledTaskOnce(keepAlive, 10,
>                      TimeUnit.MILLISECONDS);
>                  Object object = scheduledTaskOnce.get();
> 
> Note: newScheduledTaskOnce() calls ScheduledFuture<?> future = executorService.schedule(runnable, delay, timeUnit);
> 
> Q1: The KeepAlive hangs when doing it as a onetime task in the same executor. Any ideas why?
> Q2: How will a onetime task in same scheduledExecutor be handled when we have a repeatedly ongoing?

You haven't specified what is your ScheduledExecutorService 
configuration/implementation.

I'm using the following in a real world project:

import java.util.concurrent.*;

     public static void main(String[] args) throws Exception {
         ScheduledExecutorService executor =
                 Executors.newSingleThreadScheduledExecutor();

         executor.scheduleAtFixedRate(slowTask("Regular", 10),
                                      0, 100, TimeUnit.MILLISECONDS);

         ScheduledFuture<?> oneOff = executor
                 .schedule(slowTask("One-off with delay", 50),
                           100, TimeUnit.MILLISECONDS);
         oneOff.get();

         executor.execute(slowTask("Immediate one-off", 100));

         Future<?> oneOff2 = executor
                 .submit(slowTask("Immediate one-off with result", 100));
         oneOff2.get();

         Thread.sleep(50);

         executor.shutdown();
     }

     static Runnable slowTask(String name, long timeMillis) {
         return () -> {
             System.out.append(name).print("...");
             try {
                 Thread.sleep(timeMillis);
             } catch (InterruptedException e) {
                 Thread.currentThread().interrupt();
                 throw new IllegalStateException(e);
             }
             System.out.println(" done.");
         };
     }

That is a single-thread scheduled executor [1] to serialize both:

   * A task scheduled to run at regular intervals; and
   * One-off executions.

> Q1: The KeepAlive hangs when doing it as a onetime task in the same executor. Any ideas why?
> Q2: How will a onetime task in same scheduledExecutor be handled when we have a repeatedly ongoing?

One of my uses actually triggers one-off task at the end of the 
scheduled task, also – not just externally submitted.  Not sure what 
"onetime task in the same executor" in you case means.

[1] 
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newSingleThreadScheduledExecutor--

-- 
Stanimir

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How to send a onetime scheduled task to executorService that has a repeptitive task ongoing mike <mikaelpetterson@hotmail.com> - 2022-03-10 04:32 -0800
  Re: How to send a onetime scheduled task to executorService that has a repeptitive task ongoing "Jeffrey H. Coffield" <jeffrey@digitalsynergyinc.com> - 2022-03-10 07:21 -0800
  Re: How to send a onetime scheduled task to executorService that has a repeptitive task ongoing Stanimir Stamenkov <s7an10@netscape.net> - 2022-03-10 22:16 +0200

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